Taxonomic issues of the genus Betula

Abstract

Birch (Betula L.) is a genus of approx. 60 species, subspecies or varieties with a wide distribution in the northern hemisphere. Understanding of systematics and evolution of this taxonomic group is of high practical importance, since most of the genus birch species are actively used in various industrial sectors and reforestation projects and are important forest tree species. The genus birch is considered to be one of the most complex among angiosperms. Taxonomy of birches has been revised several times, but systematic position of many representatives of the genus birch is being reconsidered today. Despite multiple comprehensive studies involving both morphological and molecular approaches a lot of unsolved issues remain in systematics and phylogeny of the genus birch. Main reasons for this include high variability of morphological characters, polyploidy, and intensive and widespread hybridization, which hampers identification of species. The purpose of the study is taxonomic analysis of the genus birch. Article discusses the features of birch introgressive hybridization, the origin of some species, summarizes the results of several molecular phylogenies based on various chloroplast and nuclear markers, and also lists birch representatives, whose taxonomic position is not confirmed by molecular genetic studies and requires additional study of natural populations using molecular markers. Various methods are used to determine the relationship between birch species: classical morphology analysis, chromosome number analysis and molecular genetic methods. One group of methods is not enough to clearly determine systematic position of some representatives of the genus birch. Therefore, the approach to the taxonomy and phylogeny of birches should be complex, using various modern methods complementing each other.

Keywords

• birch
• phylogenetic tree
• hybridization
• taxonomic review
• molecular markers
• molecular phylogeny